Embodiments of the invention generally relate to impulse-reduction devices on breakable plunger rod assemblies for medical devices, such as syringes.
The re-use of medical equipment that is intended to be single-use is a source of great concern, because such re-use can lead to the transfer of contagious diseases. Syringes comprising a syringe barrel having an elongate tip and a fluid passageway, which is typically the lumen of a needle attached to the syringe through which fluid exits the syringe, are an example of such devices. Such syringes further comprise a plunger having proximal end upon which a user applies force to advance the plunger into the barrel and a proximal end with a distal portion. After use, some amount of fluid typically remains in what is referred to as dead space between the distal portion and the elongate tip of the barrel.
Attempts have been made to prevent the re-use of syringes by providing breakable plunger rods as part of the syringe assembly, examples of which being disclosed in U.S. Pat. No. 6,217,550 (Capes), the entire content of which is incorporated herein by reference and in U.S. patent Publication Number US 2004/0199113 (Capes et al.), the entire content of which is also incorporated herein by reference. Such breakable plunger rod assemblies provide a breakable connection between the main body of the plunger rod and the proximal distal portion. Such breakable connections possess sufficient structural integrity to resist breakage during normal use, but break upon application of additional force. Thus, after injection of the liquid contents of the syringe into a patient or into a suitable container or device such as through the pierceable septum of a catheter connector, a user applies additional force on the thumb press of the plunger rod. This additional force causes the breakable connection to shear, mechanically disconnecting the main body of the plunger rod from the distal portion, and hence disabling further use of the syringe.
After the breakable connection activates (i.e., breaks), the main body of the plunger rod moves forward at a relatively high speed and strikes the distal portion. This creates a contact impulse that compresses the distal portion and forces out fluids that remain within the dead space between the distal portion and the passageway of the elongate tip of the medical device. These fluids can be expelled at high speeds, resulting in a spray from the tip of the opening or lumen if a needle is attached to the syringe. Such a spray poses a risk of spreading contaminating fluids or blood.
It would be therefore desirable to provide syringes and breakable plunger rod assemblies that mitigate the risk of liquids spraying from the nozzle of a medical device when the plunger rod is disabled.